Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $210.49   11.478%   $234.65   $234.65   $234.65   $234.70  
  Purchase #2 $65.28   4.197%   $68.0198   $68.02   $68.00   $68.00  
  Purchase #3 $116.75   6.113%   $123.8869   $123.89   $123.90   $123.90  
  Purchase #4 $141.80   11.214%   $157.7015   $157.70   $157.70   $157.70  
  Purchase #5 $84.58   10.796%   $93.7113   $93.71   $93.70   $93.70  
  Purchase #6 $228.61   4.412%   $238.6963   $238.70   $238.70   $238.70  
  Purchase #7 $164.44   7.628%   $176.9835   $176.98   $177.00   $177.00  
  7 purchase totals = $1,011.95       $1,093.6493   $1,093.65   $1,093.65   $1,093.70